On a remote stretch of the Mekong River in northern Laos, the silence is broken by the dull boom of dynamite. This is the site of the Xayaburi Dam, the first dam being built on the main stem of the river south of the Chinese border.

Concrete terraces now climb the steep riverbanks, and engineers estimate the project is one-third complete. If work remains on schedule, the 107-foot-tall (33 meters) Xayaburi will block the river by February. As the dam rises, however, the controversy around it is deepening.

The Xayaburi is endorsed by the Laotian government, which has stated its ambition to become the "battery of Southeast Asia," and financed by Thai investors who are eager to supply their nation's booming cities with electricity. But the project, along with several other large dams proposed downstream, are vehemently opposed by Cambodia, Vietnam, and many environmental organizations because of their threats to the river and those who depend on it.

The Mekong, which roughly translates to "mother of water" in the Lao and Thai languages, is the longest river in Southeast Asia. Running for more than 2,700 miles (4,345 kilometers) from the Tibetan Plateau to its delta in southern Vietnam, it is the largest inland fishery in the world and an essential part of the region's food supply: An estimated 50 million people live on the free protein its fish provide.

"The dams would be a disaster of epic proportions," says Kraisak Choonhavan, a longtime Thai politician and progressive activist.

NG Staff; Source: International Rivers

Villagers from Khok Yai travel by boat and foot to work on the Xayaburi Dam. Once the dam is finished, the village will be evacuated and its residents relocated.

Court Challenges

In June, the Xayaburi Dam's opponents were strengthened when a Thai national court agreed to hear a lawsuit by 37 villagers who are challenging the Thai government's plans to buy most of the power.

The villagers who brought the suit live along the Mekong in northeastern Thailand, where the river forms the border between Thailand and Laos. Floods and droughts, they say, already have become more devastating because of six Chinese dams upstream. They fear that the Xayaburi and the other planned dams will not only worsen flooding, but also disrupt fish spawning and ultimately force the villagers off their land.

Northern Thailand has a well-established network of grassroots environmental and social groups, and activists there have protested the Xayaburi and other dams by holding long-distance protest marches along the river, organizing demonstrations in Bangkok, and appealing to domestic and foreign policymakers.

"We've done everything imaginable to convince the dam builders that they have to be responsible not just to Laotians, but to everyone who uses the Mekong," says Somkiat Kuenchiangsa, a leader of the northern Thai conservation group Rak Chiang Khong.

In 2012, when the villagers initiated their lawsuit against five Thai government agencies, they alleged that the government's plans to buy electricity generated by the Xayaburi Dam violated the Thai constitution and the 1995 Mekong Agreement, a nonbinding commitment to cooperative river management signed by Cambodia, Laos, Thailand, and Vietnam. In February 2013, an administrative court declined to hear the case.

At left, an extended family eats dinner by candlelight in Khok Yai. At right, a family relocated by dam construction has electric power in their new house in the village of Houyhip. Although some relocated families are enjoying modern conveniences, others have not received promised payments or housing.

The villagers appealed to Thailand's Supreme Administrative Court, and on June 24, the court agreed with their contention that the Electricity Generating Authority of Thailand, or EGAT, had failed to properly notify the public about the Xayaburi project and had not conducted an adequate environmental assessment. (EGAT has signed an agreement with dam developers to purchase 95 percent of the power; the court denied the villagers' request to cancel that agreement.) EGAT and other agencies named in the suit must respond to the allegations in the coming months, and a final decision is expected to take at least a year.

The court's recognition of the villagers' stake in the issue does not halt construction, but it has legal and financial implications for the Xayaburi, whose future depends in large part on the confidence of its Thai backers. "It may be the beginning of the use of the Thai legal system to stop dams on the Mekong—and that could create some uncertainty for investors," says Ian Baird, a geographer at the University of Wisconsin–Madison and an expert on Mekong hydropower development.

Downstream, a Second Dam Rises

About 700 miles (1,125 kilometers) south of the Xayaburi construction site, on the border between Laos and Cambodia, the Mekong roars over a jumble of basalt cliffs, forming Khone Falls—a welter of cascades and rapids whose volume is nearly double that of Niagara Falls. Next to the falls, the wooden-hulled, car-engine-powered boats characteristic of Southeast Asia buzz up and down a large side channel, and locals say the boats are carrying surveyors and engineers to and from the site of the proposed Don Sahong Dam.

For now, daily life in Khok Yai continues as usual: A child bathes under a communal spigot, and a pet monkey snacks.

Foreign investments drive new construction along the Mekong in Vientiane, the capital of Laos. The country remains one of the poorest in the world.

Like the Xayaburi, the Don Sahong is supported by Laos and opposed by Cambodia and Vietnam. The proposed site is a key migration route for many native Mekong fish species, and fisheries experts believe the dam could be more damaging to regional food supplies than the Xayaburi would be.

But as with the Xayaburi, Laos is pressing forward on the Don Sahong without the approval of its neighbors. Activists who have visited the site say its Malaysian developer, Mega First, has begun construction of access roads and a bridge.

The 1995 Mekong Agreement among Cambodia, Laos, Thailand, and Vietnam stipulated that the countries would consult each other before beginning any project with significant impact on the river, and it established the Mekong River Commission to oversee that process.

But the commission's already shaky authority was weakened by Laos's unilateral action on the Xayaburi, which violated the ten-year moratorium on main-stem dam construction recommended by the commission in 2010. Laos also has insisted that consultation on the Don Sahong is not needed because of its location in a side channel. A river commission meeting on the issue in January ended in an impasse.

In late June, the countries met in Bangkok for a final attempt to resolve the disagreement within the commission's negotiation process. At that meeting, Laos—under heavy pressure from its neighbors, including its close ally and patron Vietnam—agreed to a six-month consultation period. But construction could continue during the consultation, and the Laotian government signaled its intention to move forward.

A man checks fishing traps in the rapids above Khone Falls, the largest waterfall on the Mekong River. An estimated 50 million people rely for food on fish caught in the Mekong.

The Mekong is home to some of the world's biggest freshwater fish. Large migratory species such as this goonch catfish (Bagarius yarrelli) are already in decline, and would be further endangered by the main-stem dams.

On an island in the Mekong near the site of the proposed Don Sahong Dam, a young woman washes dishes in the shade of a roadside food stall.

"With your support and constructive input, the [Laotian] government will continue to develop the project in a responsible and sustainable manner," Viraphonh Viravong, Laos's vice minister of energy and mines, said at a news conference.

After the meeting, International Rivers and other environmental groups reiterated their calls for a construction moratorium and significant strengthening of the Mekong commission's power.

As regional controversy simmers over the Xayaburi and the Don Sahong, those who depend on the river for survival watch and wait.

In far northern Cambodia, just out of earshot of Khone Falls, the river is broad and flat, its surface broken occasionally by critically endangered Irrawaddy dolphins. Small groups of people fish from the banks and mid-channel islands with lines and nets. Sei Feng, the leader of a nearby village, has arranged some ragged tarps into a fishing camp, and there he and his family wait for their luck to turn.

"We're not catching much, but we keep trying," he says. "We keep trying, because who knows what the future will be like?"